4 Answers

You can use this conversion table to calibrate your speedometer: http://tire-size-conversion.com/speedometer-calibration/ OR you you can reprogram the ECU to make the MPH correct on the gauge with a tool like this: http://www.hypertech-inc.com/products-speedometer-calibrator.aspx

After entering your tire sizes, you're only about 2 mph off (slower) on the MPH gauge than the stock tires. Not much to worry about unless you want to get the speedometer dead accurate. Going from a 70 to a 65 series is not a huge jump so it's not that far off.

What could cause the speedometer, RPM gauge, and lights not to work?
All happened at same time and noticed when made a sharp left turn; all
the sudden that all happened along with the seatbelt light...

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